Ductile corrosion-resistant ferrous alloys containing chromium

ABSTRACT

AN IRON, 28%-37% CHROMIUM CONTENT ALLOY IN WHICH POSTWELDING DUCTILITY IS IMPROVED BY THE INCORPORATION OF SMALL AMOUNTS IN THE APPROXIMATE RANGE OF ABOUT 0.1% TO 1.0, OF AL, CU, PT, PD OR AG, OR COMBINATIONS OF AT+CU, AL+AG, AL+V OR AL+CU+V.

June 27, 1972 slpos ETAL DUCTILE CORROSION-RESISTANT FERROUS ALLOYS CONTAINING CHROMIUM Filed May 4, 1970 fikfi w u m mm mm mm Q Q IE fi I $5 a a 0 Q G Q mQ 8 mu 63* z z z um Corrosion Bate Mia/mus ilimgGfiZH/L'Og or 30121713507) H 0 WilhFe (S0 [MN T0125 8M Y Sm w M WGA uww MH o E PM w W! NM United States Patent 61 3,672,876 Patented June 27, 1972 US. Cl. 75-124 3 Claims ABSTRACT OF THE DISCLOSURE An iron, 28%-37% chromium content alloy in which postwelding ductility is improved by the incorporation of small amounts in the approximate range of about 0.1% to 1.0% of Al, Cu, Pt, Pd or Ag, or combinations of Al+Cu, Al+Ag, Al+V or Al-l-Cu-l-V.

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of US. application Ser. No. 707,350 filed Jan. 26, 1968, which, in turn, was a continuation-in-part of US. application Ser. No. 623,402 filed Mar. 15, 1967, in the names of the same applicants as joint inventors.

BRIEF SUMMARY OF THE INVENTION Generally, this invention comprises a corrosion-resistant ferritic iron, chromium alloy containing from about 28%- 37% Cr, carbon 0.03% maximum, nitrogen 0.04% maximum, and minor amounts of the elements usually present in the raw materials employed for iron-chromium alloy metallurg enriched to confer postwelding ductility by the addition of one of the group: (1) a% A, (2) 0.1- Al plus b% B and (3) 0.10.5% Al plus 0.30.7% Cu plus 01-03% V, wherein a% A consists of one of the following: substantially 0.l0.9% Al, 0.3-l.3% Cu, 0.2l.0% Pt, 0.21.0% Pd and 0.1-1.0% Ag, and b% B consists of one of the following: substantially 0.4-l.3% Cu, 0.l-0.35% V and 0.03-0.5% Ag.

DRAWINGS The resistance of ferritic iron, chromium alloys to various corrosive environments is plotted in the attached drawing, in which the corrosion rates in mils/yr. when subjected to boiling 65% HNO or boiling 50% H 50 containing Fe (SO are plotted on the left-hand ordinate axis whereas the corrosion rate in FeCl mg./

ice

(dm. (day) is plotted on the right-hand ordinate axis, versus chromium content in weight percent on the abcis- Ferritic Fe, Cr alloys are particularly advantageous in the respects:

(1) Reduced cost over austenitic Cr-Ni stainless steels because of the elimination of Ni,

(2) Excellent corrosion resistance of the high Cr content compositions to many media of industrial importance, and

(3) Improved resistance to chloride stress-corrosion cracking, towards which austenitic stainless steel is especially vulnerable.

However, experience to date has revealed that ferritic Fe, Cr alloys develop a high degree of brittleness in or adjacent to welds, and this inadequacy has severely limited all uses of the alloys containing more than about 20% Cr, where welding is essential, as, for example, in the manufacture of chemical processing and other vessels, pipes and similar equipment.

Previous investigators were able to reduce the impact brittleness of ferritic chromium alloys by limiting combined carbon and nitrogen contents to 0.02% maximum, as reported in US. Pat. 2,624,668-71; however, marked postwelding brittleness persisted and, in U.S. Pat. 2,- 624,670, it was reported necessary to convert the alloys to at least a partially austenitic state in order to cure the diificulty. But austenitic alloys are subject to chloride stress-corrosion cracking and so one valuable attribute was lost in the acquisition of another. Moreover, it was deemed necessary in the prior art to heat treat by annealing at 900 C., followed by rapid quenching, in order to minimize brittleness in weldments, and this is an exceedingly troublesome and expensive expedient.

Applicants have now confirmed that low carbon-nitrogen contents in ferritic Fe, Cr alloys are not, in themselves, sufiicient to prevent brittleness in or near unannealed weld areas; however, they have discovered that certain additional alloying metals can be added in small and very critical amounts in order to obtain high post welding ductility to a degree where annealing can be dispensed with, provided that proper welding techniques and controls are employed. Conventional inert-gas arc welding procedures were found to be entirely satisfactory. In addition, applicants have established that the cause of brittleness in ferritic Fe, Cr alloy welds is probably not grain coarsening, at least not exclusively, because many of their welds displayed a coarse-grained structure but were still found to be free of brittleness.

The corrosion resistance of Fe, Cr alloys as a function of Cr, C and N content is set out in the following Table 'I, with the results plotted in the figure.

Corrosion rates Chromium content 50 wt percent percent Wt. percent P.p.m H2304 b wt. FeCla Fe2(SO4)a percent (mg .ldm .2/ Nominal Actual C N (mils/year) HNO day) B Wrought, annealed (30 mins. at 850 C. with water quench) pecimens, unwelded.

The three corrosion tests utilized evaluated weight loss in mg./dm.'*/day towards 10% FeCl .6H O solution (righthand ordinate axis), and corrosion rate in mils/year towards ferric-ion inhibited boiling 50% H 80 and boiling 65% HNO; individually (both on the left-hand ordinate axis), versus weight percent chromium on the abscissa.

-For best corrosion resistance, Fe, Cr alloys containing at least 28% by weight of chromium should be employed, good results beingobtained where the carbon content is 0.03% maximum and the nitrogen content is 0.04% maximum, each being preferably lower than the maxima reported. Thus, as hereinafter detailed, a carbon content of 0.01% maximum and a nitrogen content of 0.015% maximum are both positively beneficial for enhanced corrosion resistance. The alloys may also contain minor amounts of manganese, silicon, phosphorus and sulfur, as well as other elements usually present in the raw materials employed for iron-chromium alloy metallurgy. The additives proposed for elimination of postwelding brittleness according to this invention do not perceptibly affect the corrosion resistance propensities of the Fe, Cr alloys as a class.

The following additives (all percentages being by weight), denoted over their essential ranges as groups, have been found individually effective as postwelding brittleness preventers:

Group 1Al, 0.1-0.9%

Group 2Cu, 0.31.3%

Group 3A1, 0.1-0.5% together with Cu, 0.41.3%-

Group 4-Al, 0.1-0.5% together with Cu, 0.3-0.7%

together with V, 0.1-0.3%

Group 5-Al, 0.1-0.5% together with Ag, ODS-0.05%

Group 6-Al, 0.1-0.5% together with V, 0.1-0.35%

Group 7-Pt, 0.2 to 1.0%

Group 8--Pd, 0.2 to 1.0%

Group 9Ag, 0.1 to 1.0%

The criticality of the percentage contents reported as regards bend test performance is demonstrated by a tabulation (Table H) hereinafter set forth of 22 difierent 35% Cr content compositions which were prepared to establish the applicable composition limits.

The reasons for the postwelding ductility enhancement conferred by this invention are not well understood; however, there is no doubt that a decided benefit is obtained, as demonstrated by the following examples. In all cases, brittleness was evaluated by bending, or attempting to bend, flat welded samples through angles of 180 along a line transverse the weld axis (except as indicated in Example 15) using standard guided bend test apparatus as provided in the ASME Pressure Vessel Code, 1965, section 9, p. 59.

The alloy specimens were each identified by a specific Sample No. for correlation in a summary tabulation hereinafter set forth.

The iron component of all of the samples consisted of Plast Iron Grade A 101 (manufactured by the Glidden Company) which typically contained the following amounts (all in weight percentages) of the six usual accompanying ingredients: C, .002%, N, .004%, Mn, 0.002%, Si, 0.005%, S, 0.004% and P, 0.005%.

The chromium content was incorporated either as chromium, or as ferrochrome (for the 038 sample series only), and the typical analyses for the several specimen sets were as follows:

SPECIMEN NUMBER GROUPS 1 Ferrochome.

Specimens 038-11 and 13 Ola-9, 10, 15 and 16- From the foregoing, it can be seen that the accompanying ingredients were present in relatively minor amounts.

The smaller alloy speciments were prepared by a skull melting technique (i.e., Examples 1-4, inclusive) employing a water-cooled copper crucible with heating accomplished under reduced helium pressure by an are maintained between the charge and a tungsten electrode disposed near the top center of the charge, so that the melt was effectively insulated against pick up of metal from the crucible walls. In Examples 57, inclusive, magnesia crucibles with vacuum-induction heating were utilized. Unless otherwise detailed, sample preparation was standardized, in that all specimens hot-worked (hot rolling for Examples 1-4, inclusive, and hot rolling plus hot forging for Examples 5-7, inclusive) at 930-1100 C. to about 50% of original thickness, except that all samples 0.10" or less in thickness had been finally cold-rolled from twice that thickness, after which the sheets were annealed for "/2 hr. at 850 C. and water quenched to relieve stresses and promote uniformity.

Example 1.A control Sample No. 011-9 incorporating no additive This melt consisted of 210 gms. of high purity chromium and 390 gms. of electrolytic iron. The final sheet thickness was 0.100".

A fusion weld was made on a piece of the alloy using the standard gas-tungsten arc welding process and an energy input per pass of approximately 16,000 joules/in, the energy input per pass in joules/inch=arch voltagex arc current/ torch travel speed, in./ sec. In further explanation, there was no joinder of two pieces of alloy here, the electrode simply being given a single pass longitudinally of the sample piece, which measured approximately 4" long x A" wide x 0.1" thick. During this pass, the energy input was sufi'icient to melt the metal in the immediate region of the electrode traverse for the entire thickness of the sample and for a width of approximately 05 When the welded strip was subjected to the guided-bend test specified for Ms" thick specimens, it fractured.

Analysis showed the alloy had a N content of 0.004% and a C content of 0.001%.

Example 2.-Aluminum additive employed (Sample No. 011-10) This melt consisted of 210 gms. of high purity chromium, 1.2 gms. of laboratory grade aluminum and 389 sf electrolytic iron. The final sheet thickness was A fusion weld was made on a piece of the alloy by the same technique employed in Example 1. The welded strip bent through 180 without fracture when subjected to the same guided bend test as for Example 1.

Analysis showed the alloy contained 0.20% Al, 0.005 N and 0.002% C.

Example 3.-A control Sample No. 041-16 incorporating no additive This melt consisted of 175 gms. of commercial purity chromium and 325 gms. of electrolytic iron. The final sheet thickness was 0.100.

A fusion weld was made on a piece of the sheet using the same technique employed in Example 1. When the welded strip was subjected to the same guided bend test as described for Example 1, it fractured.

Analysis showed the alloy contained 0.006% C and 0.005% N.

Example 4.Copper additive employed (Sample No.

This melt consisted of 175 gms. of commercial purity chromium, 3.75 gms. of laboratory grade copper and 321 gms. of electrolytic iron. The final sheet thickness was 0.100".

A fusion weld was made on a piece of sheet using the same technique employed in Example 1. When the welded specimen was subjected to the same guided bend test as described for Example 1, it bent 180' without fracture.

Analysis showed the alloy contained 0.75% Cu, 0.02% C. and 0.005 N.

Example 5.A control Sample No. 215 incorporating no additive This melt consisted of 7,937 gms. of commercial purity chromium and 14,741 gms. of electrolytic iron. Vacuuminduction melting was followed by consumable vacuumarc melting to produce an ingot which was hot-forged at 930-1100 C. to a 3" thick slab. This slab was thereafter hot-rolled at 9301100 C. to a plate thick, which was annealed for /2 hour at 850 C. and water quenched.

Elongated pieces of this plate were double-beveled to a V edge, the pieces clamped to hold the V edges closely adjacent one another and then fusion-welded with filler metal made from the same alloy and an energy input of 35,000 joules/in. per pass. Several passes were used to again attain the original thickness, or slightly above. When the welded plate was bent in the guided-bend test with fixture for /s" plate, it fractured.

The alloy contained 0.004% C and 0.004% N.

Example 6.Copper, aluminum and vanadium together incorporated as additive (Sample No. 216) This melt consisted of 7,937 gms. of commercial purity chromium, 90.7 gms. of laboratory grade copper, 56.7 gms. of laboratory grade aluminum, 6.7 gms. of laboratory grade vanadium and 14,537 gms. of electrolytic iron which was first vacuum-induction melted together in a magnesia crucible, followed by vacuum-arc melting as in Example 5. The ingot from this second melting was hotforged (930-1100 C.) into a 3" thick slab, then hot rolled ,(930l100 C.) to a thick plate. The plate was annealed for /2 hour at 850 C. and water quenched.

Pieces of the plate were fusion welded, using the technique described in Example 5 and filler metal made from the alloy. Under the weld test utilized in Example 5, the specimen survived 180 bending without fracture.

The alloy contained 0.25% Al, 0.25 V, 0.4% Cu, 0.004% C. and 0.004% N.

In addition to the alloys described in Examples 1-6, a large number of other Fe, Cr alloy compositions of generally the same basic analysis were made up and tested using similar techniques. The following tabulation summarizes the results obtained:

TABLE IL-EFFECT OF MINOR ALLOYING ELEMENTS ON THE POSTWELD DUCTILITY OF FE, 35% CR ALLOYS Bend test A after No. Additive percent percent welding 011-9 None 0. 001 0. 004 Fracture. 041-16- 0. 006 O. 005 Do. 215. 0. 004 0. 004 Do. 042-12 0. 005 0. 004 Do. 042-13- 0. 005 0. 004 0. 002 0. 005 180. 045. 3. 0. 003 0. 007 180.

0. 004 0. 004 Fracture 0. 02 0. 01 D0 0. 005 0. 0005 180. 0. 02 0. 005 180. 5% Cu 0. 003 0. 005 Fracture 0.2% Al plus 0. 3% Cu 0.002 0. 009 Do 0. 2% Al plus 0. 5% Cu 0. 002 0. 004 180. 0. tlcplus 0.3% V plus 0. 004 0. 01 Fracture.

. 0 u. 216 0. 25% A1 plus 0. 25% V 0. 004 0. 004 180.

plus 0. 4% Cu. 0 0. 007 0.03 Fracture. 0. 2% Al plus 0. 01 0. 03 180. 0. 5% Pt--- 0. 004 0. 003 180". 5% Pd" 0. 007 0. 004 180. 0. 5% Ag- 0. 006 0. 004 180. 044-9 2. 5% Mo 0. 005 0. 002 Fracture.

Example 7.-Mechanical properties comparison test This test was conducted to determine the effect of minor alloying elements on mechanical properties other than postweld ductility for Fe, 35% Cr alloys.

The control Sample No. 215 of Example 5 incorporating no additive was compared with Sample No. 216 of Example 6 containing the three metal Cu, Al, V combination additive. The tensile tests were run at a strain rate of 2 in./in./min.

0. 2% Ultimate yield tensile Percent strength, strength, reduction Alloy Heat treatment p.s.i. p.s.i. in area 215"... hr. at 850 C. and fur- 68, 400 85, 800 7. 4

nace cooled. 216 do 73, 000 86, 900 55 215.... hr. at 850 C. and 57, 200 75, 800 70 water quenched. 216 .-do 50, 700 70, 900 67 It will be seen that the Fe, Cr alloy with additive (Sample No. 216) displayed about the same mechanical properties as the control Sample 215 after annealing and water quenching; however, furnace cooling made Sample 215 brittle but Sample 216 resisted this embrittlement.

Example 8 This was an additional mechanical properties test involving the fabrication of a tube outside dia. x 30" long employing typical sheet-metal Working practices without special precautions.

The material used was thick alloy No. 216 (Example 6), hot rolled at 9301100 C. to 0.10" thickness, followed by cold-rolling to 0.05" thickness, with final annealing for /2 hour at 850 C. and water quenching.

The seam of the tube was welded using standard inert gas arc-welding technique and filler metal of the same alloy composition as the tube.

The tube tested watertight (under the static head of water filling the vertical tube) and could be collapsed on itself without fracture. In contrast, thin sheets of alloy No. 215 (Example 5) fractured when bent after welding.

Since the most important commercial field of use for high chromium-iron alloys is in corrosive environments, due to the exceptional corrosion resistance of these materials, it was vital to determine whether the employment of any of the additives of this invention reduced corrosion resistance, and the following Examples 9-13, inclusive, were devoted to this investigation.

Example 9 The test specimens were prepared in accordance with the procedures of Example 3 for the control Sample No. 041-16, and Example 5 for alloy No. 215, containing no additives, whereas the procedure of Example 4 was followed for the additive-containing specimens. The corrosion test procedure adopted was that set out in ASTM A262-64T (1965 Book of Standards, pp. 217-239) employing boiling 50% H 80 containing ferric sulfate (conc. 41.6 g./l.) with the exposure period doubled to 240 hours instead of the 120 hours standard limit. The results are summarized in the following Table HI:

TABLE III.CORRO1SBON RATES OF MODIFIED Fe. 35% Or ALLOYS AFTER 240 HOURSE BOILING 50% H2304,

FERRIC SULFATE EXPOSURE TEST Corrosion ra Additive (in/mo.)

0.4 Cu plus 0.25 V plus 0.25 A1.

216 (welded) do A.I.S.I. Type 304 (18-8 (stainless steel).

From these tests, it appears that the additives provided according to this invention have no adverse eflects on corrosion resistance.

Example A particularly severe pitting corrosion environment is that of 10% Fe'Cl -6H O in water solution. Investigations graphically represented in the figure have shown that the chromium content of a substantially pure Fe, Cr alloy should exceed about 28% by weight in order to achieve a dependable low corrosion rate here. The points plotted reveal the beginning of a steep rise in corrosion propensity at chromium contents below about 28%, whereas there is a decided fall-01f in this regard with increase in chromium above about 28%. Immediately above the 30% Cr level the corrosion rate for all tests conducted was very low.

Alloy 216, consisting of Fe, 35% Cr, to which was added 0.4% Cu+0.25% Al-|-0.25% V, was similarly tested and showed zero measurable weight loss after 10 days exposure according to this test.

Example 11 The resistance of Fe, Cr alloys to boiling ferric-ion (conc. 41.6 gm./l.) inhibited 50% H 80 and to boiling 65% HNO respectively, is plotted in the figure (left-hand ordinate axis) and confirms that Cr contents above about 28% are desirable for lowest corrosion rates.

Alloy No. 216 tested in these same environments showed exceptionally good corrosion resistance, in that the measured corrosion rate was only 0.0006"/mo. in the boiling inhibited sulfuric acid and 0.0003"/mo. in the boiling nitric acid. Thus, the presence of the additives was not found to reduce the corrosion resistance perceptibly.

Example 12 Comparative corrosion resistance towards boiling 10% H was evaluated in the following test series:

BOILING 10% H2804 Corrosion rate Alloy: (in./mo.) A.I.S.I. 1 446 (27% Cr in Fe) 34 A.I.S.I. 1 304 (18% (Jr-10% Ni) 1.6

Chloride stress corrosion propensity was tested employing boiling 42% MgCl solution on stressed U-bend specimens according to a procedure described by I. H. Phillips and W. J. Singley in Corrosion, September 1959.

The austenitic steel A.I.S.I. Type 304 survived this test only 1.5 hours before cracking, whereas both Fe, 35% Cr alloys No. 215 (without additive) and No. 216 (with additive) survived 550 hours immersion without cracking.

The incorporation of additives according to this invention has proved to be advantageous for Fe-Cr alloys having chromium levels below those preferred for best corrosion resistance, as the following example demonstrates:

Example 14 Specimen 037-17 consisted of a typical A.I.S.I. 446 alloy nominally containing 27% chromium, which was remelted under vacuum to lower the carbon and nitrogen contents to the levels of 0.04 weight percent each, whereas specimen 037-16 was the same material modified by vacuum remelting and the incorporation of 0.2% A1, 0.3% V and 0.5% Cu (all weight percents), the carbon content of the latter analyzing 0.05% by weight whereas the nitrogen was 0.04% by weight.

The specimens were prepared in the standardized manner detailed for Example 5, with final sample thickness of 0.10".

Then the specimens were each cut into four pieces, these pieces being about 4" long x A" wide x 0.1" thick, and longitudinal fusion welds made on each piece in the manner detailed for Example 1.

Following this the pieces were air-cooled and two each were tested by bending transverse the weld, whereas the remaining two were tested with bending force application parallel to the welds and approximately downthe axial center lines of the welds, using the standard guided bend test apparatus described in the ASME Pressure Vessel Code, 1965, Section 9, p. 59.

The 037-16 composition (modified by incorporation of additives according to this invention) passed the axial force application postweld ductility tests, and one sample passed the transverse bending test while one sample failed this test, whereas the 037-17 composition pieces failed both postweld ductility tests.

A repeat test was conducted on four pieces of a specimen identified as (050-33), which incorporated approximately 30% Cr, plus the additives 0.5% Cu, 0.2% A1 and 0.3% V -(al1 weight percents), prepared as a 0.10" thick sheet, cold-rolled and then annealed at 930-1100 C. (C content 0.005% by weight, N 0.01%). The pieces were subjected to both parallel and transverse postwelding ductility tests and all passed.

Example This example shows the importance of carbon and nitrogen content as regards corrosion resistance, and demonstrates the importance of limiting the carbon to about 0.01% by weight maximum and the nitrogen to 0.015% by weight maximum.

The corrosion test procedure followed was the ASTM A262-64T (1965 Book of Standards, pp. 2.17239) test which was employed in Example 9, i.e., utilizing boiling )50% H 80 containing .ferric sulfate (conc. 41.6 g./l.

The specimens were all Fe-Cr alloys, each containing nominally 35% Cr, some with the additives hereinafter tabulated and some without additives. Three different heat treatments were utilized for comparative purposes: (1) denoted S.C. (i.e., slow cooling) involving heating for one hour at 1100 C. followed by slow cooling, the latter constituting cooling immersed in a small amount of heat-retaining sand to cause the relatively small samples to simulate the normal air-cooling which larger weldments customarily undergo in industry, (2) denoted W.Q., involving heating for one hour at 1-100 C. followed by water quenching and (3) denoted Annealed, involving heating for 30 minutes at 850 C. followed by water quenching. The tabulation reports the corrosion rates in mils/year (120 hours immersion period).

Weight in grams,

Sample No.-

Ingredient 524A 525A H.P.Cr flakes. 308 318 Plast iron. 684 670 Copper... 5. 0 5. 0 Aluminum 4. 0 High 0 ferrochrome..- 1. 26 1. 26 High N ferroehrome..- 2.44 2.44

The alloys were vacuum induction melted as 1000 gm. ingots. The ingots were forged and hot rolled at 1100" Specific sample analysis. 1 Dissolved completely.

On the basis of the foregoing, both the relatively high N alloy 037-4 and the high C+ high N alloy 037-40 performed poorly in the corrosion test, whereas the modernate C and N alloy 050-1 performed comparatively better. Nevertheless, even lower C contents of 0.01% by weight maximum and N of 0.015% by weight maximum are preferred.

Example 16 This example shows the postwelding ductility obtained by controlled additions of Al and V. All specimens were prepared in the manner hereinbefore taught for specimen 050-33, Example 14, except that the chromium content was nominally by weight.

0.1" thick speci- Wt. percent P.p.m. men, transverse post weld V Al C N Duetility 0. 2 0. 3 270 126 180 0. 3 0.2 42 48 180. 0. 3 0. 5 45 120 180 (2samples); 0. 5 1. 0 75 289 Fracture. 0. 5 1. 0 127 353 D0.

From the foregoing, it is apparent that Al+V is effective in imparting postwelding ductility, these and other experiments placing the effective limits at about 0.1- 0.5% A1 together with 0.'l-0.35% V.

Example 17 This example reports various tests made on specimens falling in the low part of the chromium range of this invention. The specimens were all given autogenous welds, as hereinbefore described for Example 1, and were tested for corrosion (mils/yr.) in the as-welded state by exposure to boiling 50% H 80 containing ferric sulfate (for 120 hours), as described for Example 9. Separate specimens were subjected to the ASME guided bend test hereinbefore detailed, all tests being made transverse the weld.

C. to a thickness of 0.25", after which they were cold rolled to 0.1", annealed 30 mins. at 850 C. and water quenched. The specimens were welded and tested for corrosion resistance and postweld ductility as hereinabove described for Sample Nos. 412E and 417E.

As welded ro erties Weightpercent P.p.m. p p Sample Corrosion No. Cr Cu Al O N resistance Bend test 524A 31.7 0.50 88 126 2 1 525A 32.9 0.41 0.38 62 200 97 ISof es) The foregoing specimens were deliberately prepared at relatively high C, N contents to confirm the eificacy of the Cu and Cu+A1 additives for the impartation of postwelding ductility under these adverse conditions. The additives are seen to be completely efiective.

The corrosion resistance for Sample Nos. 524A and 525A was not equal to that of specimens 512E and 417E, due to the relatively high C+N contents, coupled with the associated low Cr contents. Moderate intergranular corrosion at the welds was also observed.

Example 18 This example was directed to the ascertainment of the maximum chromium content within which the additives of this invention are efiective in the impartation of postwelding ductility. Nitrogen contents were deliberately carried on the high side to assure the determination of a conservative chromium maximum. All specimens were rolled to final 0.1" thickness, annealed for 30 minutes at 850 C. and water quenched prior to autogenous welding and, finally, transverse bend testing.

Wt. percent P.p.m. Postwelding Al C N bendtest 0.33 67 338 180. 0.40 13 329 180. 0.37 15 367 Fracture. 0.39 8 413 Do. 0.33 15 418 Do.

Wt. As welded properties percent P.p.m.- Corrosion Sample No. Cr Al O N resistance Bend test 417E 30.2 0.72 5 61 7.2 180 (3 samples). 412E 28.0 0.64 5 103 12 D0.

11 12 tive at chromium levels as high as about 37% by weight. which the species of said group is substantially 0.25%

What is claimed is:- A1+0.40% Cu+0.25% V. 1. An iron, chromium alloy having postwelding duc- 3. An iron, chromium alloy according to claim I havtility consisting essentially of iron, chromium in the range ing a carbon content of y weight maximum and of about 7 carbon 0.03% maximum nitrogen 5 a nitrogen content of 0.015% by weight maximum. 0.04% maximum and minor amounts of the elements R f d usually present in the raw materials employed for irone erences I e chromium alloy metallurgy, plus one of the group: UNITED STATES PATENTS (1) 11% A, 10 2,232,705 2/1941 H1111 75124 (2) (ll-0.5% ALI-5% B and 3,285,738 11/1966 IOhIlSOn 75-125 (3) (Ll-0.5% Al+-0.30.7% Cu+0.13.0% V, where- 2,624,671 1/1953 Binder 75-126 R in a% A consists of one of the following: substan- 2,752,233 6/1956 Walton 75126 R tially 014.9% Al, 034.3% Cu, o.2 1.o% Pt, 3,065,067 11/ 1962 Aggefl 0.2-1.0% Pd and 0.1-1.0% Ag, and b% B con- 15 HYLAN B O sists of one of the following: substantially O.4-1.3% D 12 Pnmary Exammer Cu, 0.10.35% V and ODS-0.5% Ag. U s L 2. An iron, chromium alloy according to claim 1 in R 

